A method to produce highly crystalline carbon powders in the shape of graphene flakes was described by Pristavita et al using the plasma decomposition of methane [R. Pristavita et al., Plasma Chem Plasma Process, 30: 267-279, 2010]. Modelling and experimental optimization enabled the ability to obtain pure, homogeneous, and well-crystallized powders having between 5-15 graphitic layers (10 layers being typical) and in-plane dimensions of roughly 100×100 nm. The high surface area and the crystallinity of the graphene nanoflakes (GNFs) made them good candidates to support catalytic sites.
The GNFs of Pristavita focused on adding nitrogen functionality through the addition of nitrogen in the main plasma stream during the GNF nucleation phase. This resulted in low nitrogen contents below 2 at % [R. Pristavita et al., Plasma Chem Plasma Process, 31: 393-403, 2011]. In a follow up study, these N-GNFs were extracted and functionalized with iron by a wet chemical method for use as replacement of the platinum catalyst typically used in fuel cells. The catalyst obtained showed both activity and full stability towards the oxygen reduction reaction (ORR) over 100-hour tests in polymer membrane fuel cells (PEM-FC) [P.-A. Pascone et al., Catalysis Today, 2013]. The iron functionalization step relied on the dispersion of GNFs in a mixture of water and ethanol; however the hydrophobic nature of GNFs made iron incorporation inefficient because of the partial agglomeration of nanoparticles in solution.
There is a need for a hydrophilic version of GNFs that can be dispersed/suspended in polar solvents so as to reduce the problem of partial agglomeration.